Refrigerating apparatus having automatic defrosting



Feb. 12, 1957 B. B. LATTER 2,780,924

REFRIGERATING APPARATUS HAVING AUTOMATIC DEFROSTING Filed Nov. 14, 1955 FIG. I

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BRUCE B. LATTER HIS ATTORNEY United States Patent REFRIGERATING APPARATUS HAVING AUTOMATIC DEFROSTING Bruce B. Latter, Louisville,

Ky., assignor to General Elec' tric Company,

My invention relates to refrigerating apparatus and more particularly to refrigerating apparatus provided with automatic defrosting means for the evaporator or chilling unit.

In refrigerating apparatus employed for the storage of foodstuffs, it is a known practice to provide auxiliary heating means to melt the accumulated frost from the evaporator or chilling unit. This heater is usually energized after a predetermined period of operation of the apparatus or simply after a timed interval, which period or interval is indicative of the formation of an excessive amount of frost on the evaporator which must be removed in order to obtain efiicient operation of the apparatus. It is necessary, of course, to provide some means for terminating the defrosting period when the frost has been removed. A practical arrangement for detecting the complete removal of frost is to provide an expansible-luid thermostat including a bellows and a bulb in thermal contact with the evaporator. the temperature rise in the evaporator is detected by the bulb and expands the bellows to terminate the defrosting operation through associated switching means. The satu- The increase in fluid pressure resulting when rated vapor-filled thermostat has been preferred to the liquid-filled because of its lower cost and permissive lighter construction. At the coldest point in the vapor-charged thermostat (the bulb on the evaporator during normal refrigerating operation of the unit) there is a partial condensation of the vapor. the coldest point establishes a vapor pressure which is indicative of the true evaporator temperature. However, since the bellows and most of the tubing which connects the bellows to the bulb are remote from the bulb, the energization of the defrost heater surrounding the evaporator to effect defrosting produces a higher temperature inthe bulb than in the tubing and bellows. This temperature distribution results in an occurrence of the partial vapor condensation with its accompanying vapor-liquid gas boundary at some 'point'in the vapor-charged thermostat other than at the bulb thus producing a pressure indicationat the bellows which is not a true indication of evaporator temperature.

Accordingly, it is an object of my invention to provide a new and improved arrangement for automatically controlling the defrosting of the evaporator unit of a refrigerator having auxiliary evaporator heating means and which utilizes. .a vapor-charged thermostat responsive to evaporator temperature.

It is another object of my invention to provide a novel arrangement for accurately sensing evaporator temperature with a vapor-charged thermostat so as to terminate the evaporator defrosting operation in a refrigerator at substantially the moment when the accumulated frost has been removed.

It is still another object of my invention to provide an improved, automatic, defrosting control arrangement utilizinga vapor-charged thermostat responsive to the evaporator temperature in a refrigerator which is compensated so as not to be adversely affected by the tem- The vapor-liquid boundary at perature of the evaporator defrost heating means relative to the ambient temperature surrounding parts of the defrost control remote from the heating means.

It is a further object of my invention to provide a new and novel control arrangement for automatically defrosting the evaporator of a refrigerator which is simple in construction, highly accurate in operation, inexpensive to construction and capable of extended operation with a resultant improvement in the operating efiiciency of a refrigerating apparatus.

In carrying out my invention, I provide defrosting heating means for the evaporator of a refrigerator which are periodically energized to melt the accumulated frost from the refrigerator evaporator surfaces. A gas-type thermostat containing an expansible vapor has a bulb in intimate thermal contact with the evaporator so that the evaporator temperature sensed by the bulb will be indicated by the vapor pressure in the thermostat. This vapor pressure actuates through associated switch means a termination of the defrosting period when the predetermined evaporator temperature is reached. I also provide means associated with my thermostat which maintain the bulb at a lower temperature during defrosting than the remaining part of the thermostat, or, in other words, will assure that the bulb is the coldest point, to give an accurate evaporator temperature reading at all times.

The novel features which are believed to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and mode of operation may be best understood by reference to the following description taken in conjunction with the accompanying drawings in which:

Fig. 1 is a partial sectional view of a refrigerator including my invention;

Fig. 2 is an enlarged view invention;

Fig. 3 is a sectional view taken substantially along line 3-3 of Fig. 2; and

Fig. 4 is a schematic diagram of the electrical circuit of my invention.

Referring now to Fig. 1, I have illustrated one embodiment of my invention having a refrigerator cabinet which includes an outer metal wall 1 and an inner metal wall or liner 2, the space between the walls being filled with partially in section of my suitable heat insulating material 3. The walls are formed to provide a door opening 4 at the front of the cabinet and a heat insulating breaker strip 5 joins the inner and outer walls 1, 2 of the cabinet in the area of the door opening 4. The inner liner 2 defines a food storage compartment 6 within the cabinet and the door opening 4 provides an access to that compartment. The opening 4 may be closed by any suitable insulated door 7.

The storage compartment 6 is refrigerated by means of a suitable mechanical refrigeration system whichineludes an evaporator 8, a compressor 9 and a condenser (not shown). The various components of the refrigeration system associated with my invention are interconnected in the conventional manner (not shown) to form a closed refrigeration system.

The evaporator 8 is located within the upper portion of the food storage compartment 6 and is preferably arranged as shown in Fig. 1 in intimate heat exchange relationship with a low temperature freezing compartment 10. It should be understood that the evaporator 8 may be arranged in any suitable manner within the compartment 6 as its location does not alfect the operation of my invention. Thus foodstuffs may be stored at below freezing temperatures in compartment 10 and the compartment 6 used for the storage of food stuffs at temperatures above freezing as it is of such capacity that it is refrigerated by the evaporator coil 8 to a lesser degree than the compartment 10. a

.the-;heater;to-begin the defrosting operation.

reases .3 During the operation of my refrigerator, the air which spills intocompartment 6 by the frequent opening of the door 7 is generally of high humidity and when cooled by the evaporator 8 itsentrainedwater vapor condenses onthe surfaces of the evaporator. Over aperiod of time this action results in abuildaup of host on theevaporator 8 which acts 'as an insulation between the evaporator surfaces and the air in the storage compartments 6, 10. This results in-a reduced .efiiciency in the operationof the refrigeration system.as less heat is removed from the "food storage compartments. ,In order toprovide for the "removal of this accumulated frost; I provide means to melt the frost from the evaporator stufaces. ,gMore specifically, I locate av heater, .11 ,inintimate .thermalcontac-t with the evaporator18,' and thei outer surfaces bf the low 'temperaturestorage compartment 10. .When-.:t he1hea ter '11 'is; energized, .the' frost is Ilmelted and .the.. r es ulti ng water maybe removedfrom.therefrigerator.inany con- "venient manner. 'Although I have preferably..shown an electrically"-operatedidefrost heater} it will.be underst o' od that any typeof heating means may. beusedlsuch as re- 'versing the flow-of refrigerant through theevaporators. For instanceg instead of energizing'aiheater 11 fwhenfdefrostinggis required, a solenoid "operated valve, may fbe provided which when energized establishes connections which reverse thefiow of refrigerant through 'the refrigeration systemI-QE vaporator 8 thus acts-asa condenser, the surfaces of which "become warm enough 'to melt Ithe --accumulated frosti Referring now to Fig. 4, 1 have shown therefrigeration compressor- 9 arranged in-a'circuit with a pair of "electri'c'al supply conductors 12, 13' which supply power to operatethe motor (not shown) to drive the compressor 9. One-side of the compressor? is connected directly to conductor-12.and the other side to a c' ont-act14. A

lswitch arm 1 pivotable at 16 is arranged to engagecon- -tact 14lin one position and thus connect the compressor to line conductor 13. In its other position, the switch arm 'lscngages'the upper contact 17 which is connected to one side of the defrost heater 11 the other side of which ais'connected. to conductor12 thus placing the heater across the supply conductors 12, 13 so that current flows through It vwill be seen that the compressor is disconnected simultaneously vfromthe ;line'with the energization' of the heater by the opening of. contact .14fand switch arm 15. W 'I- preferablyinitiate the defrosting operation byacon- .ventional clock timer 18 of which the switch arm ,15 along with contacts' l4, '17 are integral parts. This timer maybe .anyofthe well-known motor driven clock timers whichareroperable after a timed period to-produce this desired vControl-and may be connected to any source of powerforoperat-ion (not shown).* i As is well understood, 'the temperature of the evap- :oratoris an; indica tion :of .the removal of-frost from the evaporator. I "thereforeiemploy a gas typ'e' thermostat l 9syvhich is arran ed (as shown in Fig. 1) to sense the temperature of the evaporator .8i Thethermostat compr ses a reservoir or bulb 20 positioned'indntimate thermalcontact with the :evaporator 8 and connectedby means of a tube'21 to a bellows 22.(Fig. 4)".' The bellovvs 22,.tube21, .andtbulb 201define a closed-chamber for an expansible saturated vapor. 'This'gas ty e thermo- .stat maybe of any type generally Well-knowmin which the vapor'pressure withinfthe bellows 221is 'a function'of the temperature of the :bulb 2t) sothat' expansionand contraction of the bellows 22 is in' response-to increases anddecreases intemperatureof the vapor in the bulb 18 respectively. I have :not'shown in my drawing the par t cular arrangement of the bellows assemblyandiits'relationship to the timer 18 but'it is Well understood in this type of control that .the bellows 22 is preferably connected to the timer 18in aimanner sothatthe movement of the timerzswitch arm is' also controlled 'by th'e"'b'ellows. This general arrangement is clearly shown diagrammatically in Fig. 4.

As iswelltunderstood in .thevapor-type of-thermostat, there is a partial condensation of the saturated vapor in the closed vapor chamber at the coldest point in the thermostat. The vapor pressure at this gas-liquid boundary establishes the pressure in the vapor chamber which represents accurately the temperature at the point of partial vapor condensation. For this reason the bulb 20 will accurately senseevaporator temperature when located as shownin 'Fig. Lin contact with evaporator 8 as in normal refrigeration operation the evaporator is-the coldest point in the thermost'atsystem. 1m other Words, as the bulb is the coldest point in the gas-type thermostat system, the vapor-system atdhe vapor-liquid gas boundary causedby .thepartial vapor condensation represents the true evaporator temperature and the defrosting cycle is thus accurately established.

However, when the defrost heater 11 is energized, the

- temperature of the evaporator and consequently thebulb in xthermal relationship with the heater 11- and :evappreviouslytaken on the temperature ofthe'cabinet and surrounding. walls. Thus, they are-substantially unef- 'fected by the heat ofthe defrost heater 11,- and therefore remain at a temperature somewhat below the temperatur'elat the. evaporator during defrost. The temperature .of the bulb ,l20now is no longerthe lowest-temperature 30 fthermostatrsystem occurselsewhere establishing agvaporliquid boundary which produces a pressure response in Tthe'bellows' ,'22.indicative of a temperature-at a location 'othe'r than at the evaporator 8.

in the thermostat and .thepoinhof condensation-in-the Referring 'now to Fig. 2, in orderto maintain the tube 21, and the'bellows 22 at a higher temperature :than the bulb 20 during the defrost cycle,,.I provide;an-anxilia1y heating wire '23 which is arranged in adoublelength,

iinfheattransfer relationship therewith, along substantially the major portion offthermostat tube 21. Preferably,

turnslof the heater 23 are also wrappedaround thebel- 'l ows'22l as shown in Fig. 2. so that the vapor-in the bel- 'lows as well .as the tube 21 will be warmed by the heat when theheater 23 isenergized. The heating wire 23 may-be of any suitable type of flexible, insulated heating Wireandis preferably doubledba'ck as shown in Fig. 2 in two lengths in order that the two ends 24 and ZSQrnaybe 'brought to a location externally of the foodcompartrnent and wired'into the circuit of Fig. 4. As will be seen "iri'Fig. ;4,'the heating wire 23 is inparallel circuitrelation'ship with'the idefrostheater 11 and is ene r.gize d., iinulta'tneous'ly therewith. The heating wire 23 is retained in contact with the thermostat 'tube .21 by means of 'a'iflexible, insulated sheath 26 .which extends circumferentiallvof the tube from immediately adjacent the bellows 22'along'the' tube 21 it oja locatio n in theyicinity 6f 'i'vhjere" the bulb '20 is connected'ito .the tube as sh own iiniFig'fl. At 'the o'pen'end 27 of thesheath'26,;Iprovide a seal 28 which seals the end of the'she'ath to prevent-the entrynf moisture'fromthe storage compartment 6. The seal- 28' is provided with'a central bo re '29 through which the tube 21 passes.

" R is necessary to provide 'somemeans"to;dispqs e got the waterjfornied when the 'frost on the evaporator 18 and compartment 10 melts. I have provided atrongh ortray 30-arranged directly belowthe evaporator coilfiandcornpartment 10 as shown in-Fig. 1 extending across the cempartment 6 and 'slante'drearwardlysons to catch the water falling from above during defrosting. The water caught in'thetray flows rearward l y and may-be disposed of by any suitable means such as a drain pipe. I'.l 1'ave not "shown any'particular arrangement for removal of ureaermst water an d it is to'be understood that'any conventionalmeans'rnay be use'd to produce the desired type of water'disposal." ln the operation 'of my invention the clock timer18 after the termination of apredetermined period according to the defrosting requirements acts-to move the contact arm 15 upwardly openingcontact 14 and de-energizing the motor of compressor 9. The contact ann moves further to close contact 17 and thereby establish a circuit from conductors 12, 13 to the heaters 11, 23. At the same time the timer 18 ceases to operate on its timing cycle as the movement of its switch arm 15 disconnects the timer from its power supply. Thus both the defrost heater 11 and thermostat heater 23 are energized. At the instant the heaters are energized, the temperature of the evaporator 8 sensed by the bulb' 20 is lower than the remaining parts of the thermostat 19. The action of the defrost heater 11 which is of considerable wattage concentration quickly warms the evaporator 8 and the storage compartment and the accumulated frost begins to melt. This heating of the evaporator 8 and compartment 10 consequently causes the bulb 20 to rise in temperature due to its intimate thermal contact with the evaporator. Thus the bulb tends to rise in temperature above the remaining portions of the thermostat 19. However, since the heater 23 is also energized simultaneously with the defrost heater 11, the portion of the tube 21 in contact with the heating wire 23 along with the bellows 22 also rise in temperature. The heater 23 is selected of such wattage concentration that although the heater 11 is of greater wattage concentration, the smaller mass of the tube 21 and bellows 22 in contrast with the large mass of the evaporator 8 and storage compartment 10 will result in the tube 21 and bellows 22 rising in temperature at the same rate as the evaporator 8 and compartment 10.

As the accumulated frost continues to melt from the evaporator 8 and compartment 10, the temperature in the bulb 20 rises accompanied by a rise in the vapor pressure in the closed vapor chamber of the thermostat 19. During the entire defrosting operation the heater 23 has been energized to insure that regardless of the temperature rise at the bulb 20, the thermostat tube 21 and bellows 22 will constantly remain at a higher temperature than the bulb. This means that the point of partial vapor condensation in the thermostat is always at the feeler bulb to retain it as the coldest point in the thermostat 19 and a pressure reading corresponding to the true evaporator temperature is indicated at the bellows.

When the temperature in the bulb reaches a temperature indicative of the removal of all the frost from the evaporator 8 and compartment 10, the vapor pressure corresponding to that temperature produces an expansion of the bellows 22 to such an extent that the switch arm is moved downwardly disengaging from contact 17 and thereby disconnecting heaters 11, 23 from the circuit of Fig. 4 and engaging contact 14 to connect the motor of compressor 9 into the circuit for resuming the operation of the refrigeration system. The timer 18 is also once again connected into its power source to resume operation of the timer to begin operation of the refrigerating apparatus and defrost timing cycle once again.

It should be understood that in addition to controlling the operation of the defrosting arrangement of my invention and the de-energization of the compressor during defrosting, additional control means 31 which are conventional in this type of refrigerator can be provided which cycle the compressor on and off in order to maintain the temperatures in the food compartments 6 and 10 at the desired levels. This control means may, if desired, be arranged in combination with the defrosting control arrangement as shown in Figs. 1, 2 and operated in response to the temperature of the evaporator sensed by the thermostat bulb to cycle the compressor 9 during the normal operation of the refrigeration system. It should be understood, however, that my invention may be used independent of the cycling control means 31.

It will be seen that I have provided a new and improved arrangement for accurately and simply terminating the defrosting operation in a refrigerator where a vapor-charged thermostat is employed to sense evapo rator temperature. Through the use of my improved arrangement no longer can the defrosting operation'be terminated prematurely leaving unremoved frost on the chilling surfaces nor will the defrosting operation continue on past the point where the frost is completely removed resulting in an excessive warming up of the food storage compartment and possible spoiling of the food contained therein. My invention not only simplifies the operation of defrosting a refrigerator evaporator but permits the use of the preferred type of thermostat containing a saturated vapor. The use of the vapor-type thermostat results in a considerable reduction in cost over other types of thermostats.

While in accordance with the patent statutes I have described what at present is considered to be the preferred embodiment of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from my invention and I therefore aim in the appended claims to cover all such changes and modifications as fall within the true spirit scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a refrigerator, an insulated cabinet having a food storage compartment, a refrigeration system including a compressor and an evaporator for cooling said compartment, first heating means for defrosting said evaporator, defrost-initiating means to simultaneously activate said first heating means and to de-activate said compressor, pressure actuated means for de-energizing said first heating means and energizing said compressor, an expansiblegas bulb in thermal contact with said evaporator communicating and forming with said pressure actuated means a closed chamber, second heating means for heating portions of said closed chamber other than said expansiblegas bulb, said defrost-initiating means also activating said second heating means with said first heating means, said second heating means being of such capacity that said bulb is at a lower temperature than the remaining portions of said closed chamber during defrosting of said evaporator, and said pressure actuated means acting upon a predetermined temperature in said evaporator to deactivate said first and second heating means.

2. In a refrigerator, an insulated cabinet having a food storage compartment, a refrigeration system including a compressor and an evaporator for cooling said compartment, a first electric heater for defrosting said evaporator, a gas-operated thermostat including a bulb, a pres sure actuated bellows, a tube communicating said bulb with said bellows and forming with said bulb and bellows a closed chamber, said bulb arranged in intimate thermal contact with said evaporator, a second electric heater in thermal relationship with said tube and bellows, a timer arranged to periodically de-activate said compressor and energize said first and second electrical heaters, said second electrical heater being of such capacity to maintain said bulb at a lower temperature than said tube and bellows during defrosting, and said pressure actuated bellows acting upon a predetermined temperature in said evaporator to cause said timer to de-activate said first and second heaters and activate said compressor.

3. A combination as in claim 2 in which said second electrical heater is arranged in at least one double row parallel to said tube, and an insulated sheath enclosing said heater and tube.

4. In a refrigerator, an insulated cabinet having a food storage compartment, a refrigeration system including a compressor and an evaporator for cooling said compartment, a first electric heater for defrosting said evaporator, a gas-operated thermostat including a bulb arranged in intimate thermal contact with said evaporator, a pressure actuated bellows arranged without said compart- 

